Effect of Zircaloy-clad fuel rod failure on BWR core spray cooling

The first full-length, electrically heated, 49-rod, Zircaloy-clad simulated BWR fuel bundle with internally pressurized rods was spray cooled under loss-of-coolant conditions. The heater rods were internally pressurized with argon to simulate fission product gas inventory. Many perforations and severe rod distortions occurred near the center of the bundle. Nevertheless, spray cooling, initiated at a maximum cladding temperature of 1920°F, was effective in limiting cladding temperatures to ~2250°F. Electrical failure of 10 heater rods complicated interpretation of the results, and it is estimated that the maximum temperature would have been ~2360°F had the failures not occurred. The maximum coolant flow area reduction around a single rod caused by local perforations was 50%. However, this flow area reduction did not appreciably impair the effectiveness of the spray cooling system. That is, analysis performed using current General Electric (GE) loss-of-coolant technique s and heat transfer coefficients derived from stainless-steel-clad bundle tests predicted the maximum cladding temperature to within 20°F.